Mannitol or furosemide? Choice of diuretics in early postoperative oliguria

The effects of renal function of furosemide and mannitol were studied during the first 6 postoperative hours in 2 groups of patients after major abdominal surgery. A standard clearance technique utilizing long time infusion of Inutest and PAH was used. Central hemodynamics were assessed simultaneously, but are presented elsewhere. Anesthesia was performed with neuroleptic agents using a uniform technique. The study started immediately after surgery with 2 control periods. Furosemide 1 mg/kg B.W. or mannitol 0.5 g/kg B.W. was then infused at random. Renal function was followed during 8 hr. Results: The given figures represent maximal changes. Furosemide: C PAH rose from 433 to 627 ml/min (p < 0.05) while C inulin fell from 125 to 86 ml/min (p < 0.005). C Na/C In rose from 0.63 to 13.69% (p < 0.001) as did also C Cl/C In: 0.35 to 20.3% (p < 0.001), C Osm/C In: 2.10 to 15.8% (p < 0.001) and urine flow: 1.14 to 18.1 ml/min (p < 0.001). C H₂O/C In rose and became positive (p < 0.05). Mannitol: C PAH rose from 537 to 714 ml/min (p < 0.05) while C In remained stabile. C Na/C In rose from 0.62 to 2.57% (p < 0.05): C Cl/C In from 0.51 to 3.58% (p < 0.01): C Osm/C In from 2.02 to 9.1% (p < 0.001) and urine flow from 0.83 to 6.1 ml/min (p < 0.01). C H₂O/C In decreased from -1.2 to -3.47% (p < 0.001). In conclusion, both diuretics increased C PAH and urine flow. In the doses given mannitol had a smoother effect and did not impair GFR. Furosemide caused an excessive loss of sodium. Due to these findings we suggest that mannitol is the first hand diuretic in postoperative (posttraumatic) oliguria in patients without known cardiovascular disease associated with increased preload or myocardial insufficiency.